1. Field of the Invention
The present invention relates to skis, and in particular to a new vibration damped, composite snow ski.
2. Description of the Prior Art
Many recently designed skis have been constructed from a composition of several types of materials in an attempt to maximize desired characteristics such as lightness of weight, flexibility, and durability. The different materials have been positioned at various cross-sectional locations in the ski to attempt to influence these characteristics advantageously. Ski designers have recognized that a highly vibration damped ski has desirable characteristics. Efforts have even been made to construct skis which dampen the high frequency vibration or flutter that occurs during high speeds and on icy slopes thus increasing the proportion of the time the ski is actually in contact with the snow. The larger the percentage of the time a ski in contact with the snow, the easier it is to control, especially when turning. In the past, the search for means to damp vibration of a ski has been focused upon multi-layer types of skis which have an inherent damping capability as compared with skis employing an internal structural torsion box design. Torsion box skis are formed by wet wrapping fiberglass around the core of a ski. The use of a wet wrapped box, with its structural fiberglass side walls, produces a more vibration prone ski than the multi layered type ski, the resin side walls of which function primarily to seal the ski core rather than structurally strengthen the ski.
One type of known vibration damping ski incorporates a core of foamed plastic material. An example of this type of ski is disclosed in Grossauer, U.S. Pat. No. 3,372,943, wherein a foam core is encased within a top and bottom metal cover sheet and within side edge strips made from resilient material. The foamed plastic core material is said to partially dampen the resiliency of the skis.
Another ski utilizing foamed plastic in the core region is disclosed in Molnar, U.S. Pat. No. 3,861,699. In Molnar the core of the ski consists of a honeycomb structure having longitudinal cavities which are filled with foamed plastic. The honeycomb portion of the core is made from fiber reinforced, resinous plastic. The core is bonded to the bottom surface of the ski through the use of an elastic bonding medium such as an epoxy or phenolic. The particular bonding medium used is said to determine the dampening characteristics of the ski.
A second type of vibration damped ski, as disclosed by Allain, U.S. Pat. No. 3,414,279, utilizes an antivibratory member constructed from rigid plastic material formed in the shape of a downwardly open channel member. Spongy elastic strips of gummed neoprene material are used to attach the flanges of the antivibratory member to the lower portion of the ski.
A third type of vibration damped multi-layer ski utilizes viscoelastic material disclosed by Schultes, U.S. Pat. No. 3,844,576 and Boehm, U.S. Pat. No. 3,901,522. In the Schultes '576 patent, the ski includes a stretch resistant constraining layer of metal which is imbedded in a thicker and wider layer of viscoelastic material, thus isolating the constraining layer from the rest of the ski. The viscoelastic layer is positioned between the central core of the ski and the bottom surface of the ski thereby ensuring that the viscoelastic layer is positioned as far as possible from the neutral axis of the ski.
The ski in the Boehm '522 patent is constructed identically to the ski shown in the Schultes '576 patent with the exception that the constraining member of the vibration damping laminate is sandwiched below a layer of viscoelastic material and above a layer of rubber. The layer of rubber isolates the constraining layer from the bottom or running layer of the ski. The viscoelastic layer in turn isolates the constraining layer from the core and upper surface of the ski. As in the '576 patent, the constraining layer is substantially narrower than the width of the viscoelastic layer and the vibration damping laminate is again positioned as far from the neutral axis of the ski as possible.
Another example of a type of ski utilizing viscoelastic material is disclosed in Caldwell, U.S. Pat. No. 3,537,717, wherein two parallel strips of viscoelastic material are positioned longitudinally along the top surface of the ski between the bindings and tip of the ski. A constraining layer of aluminum, stainless steel or fiberglass material is positioned on top of each dampening strip.
A fourth type of ski incorporating viscoelastic material is disclosed in Head, Canadian Pat. No. 680,647. This particular ski is said to permit its bending to be independently varied from its torsional rigidity characteristics. The ski essentially includes an upper laminate, a central core and a bottom running surface. The upper laminate has a metallic top facing, an intermediate layer of rubber, and a metallic lower layer. This particular laminate construction is said to reduce the overall sheer stiffness of the ski, while not affecting the overall bending stiffness of the ski, thereby increasing the ability of the ski to absorb vibration.
Also of interest are Legrand et al., U.S. Pat. No. 4,071,264, which discloses a ski constructed from a reinforced core formed from synthetic resinous material, and Seawall, U.S. Pat. No. 3,612,556 which discloses sandwiching a longitudinal strip of neoprene material below an aluminum plate and above the ground-engaging bottom strip of a ski. Holman, U.S. Pat. No. 3,635,482, discloses a ski which has a polyurethane foam core interposed between upper and lower sheets of glass reinforced thermoplastic material.